class_docstr: Zip multiple :class:`~fairseq.data.FairseqDataset` instances together.
  
  Shorter datasets are repeated in a round-robin fashion to match the length
  of the longest one.
  
  Args:
      datasets (Dict[~fairseq.data.FairseqDataset]): a dictionary of
          :class:`~fairseq.data.FairseqDataset` instances.
      eval_key (str, optional): a key used at evaluation time that causes
          this instance to pass-through batches from *datasets[eval_key]*.
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code: def _map_index(self, key, index):
      assert (
          self._ordered_indices is not None
      ), "Must call RoundRobinZipDatasets.ordered_indices() first"
      o = self._ordered_indices[key]
      return o[index % len(o)]
  
file_path: fairseq/fairseq/data/round_robin_zip_datasets.py
imports: import logging
  from collections import OrderedDict
  from typing import Dict, Sequence
  import numpy
  from .None import FairseqDataset, LanguagePairDataset
label_desc: Use image node_id 2 for calling the RoundRobinZipDatasets obj's underlying member method code with example usage: obj._map_index(key, index) and returns: o